Nearly invisible floating oceanic predator with paralytic stingers

Giant Jellyfish are one of the more underrated dangers of the ocean. They float with the currents and the tides nearly invisible (surprising on a 1-4 on 1d6) but moving to attack any creature who passes within 30 feet of the monster. The attack of the giant jellyfish is a simple one: it drags its trailing tentacles over the body of its victim, and many tiny stingers strike, inflicting both pain and paralysis. Any living creature hit by a giant jellyfish must make save vs. Paralysis or be paralyzed for 2d4 turns. As this will naturally happen in water, a paralyzed victim may then drown. A giant jellyfish has 2d10 tentacles per hit die, and 50% of successful hits will be against the tentacles; while each point of damage severs a tentacle, only damage done to the creature's main body counts against its normal hit points. Severing all the tentacles renders the creature harmless, and they will regenerate over the course of a few weeks. Attackers who are aware of these facts may choose to attack the main body specifically, in which case any successful hit will count against the creature's hit points.